Reef Fish Census and Tagging Studies Related to Marine Protected Areas in the Florida Keys National Marine Sanctuary.
Principal Investigator: Billy Causey, National Marine Sanctuary Program

Introduction

The August 2002 Aquarius mission includes two research projects, both of which address fishes and marine protected areas in NOAA's Florida Keys National Marine Sanctuary.

Acoustic Tracking Methods Applied to Marine Protected Areas

Marine protected areas (MPAs) are recognized as an important management tool for the conservation of marine wildlife populations. There is currently a national and international effort to increase the area of the ocean under protection, as this is seen as a feasible way to help stop dwindling fish populations and catches, conserve critical habitats and biodiversity, and to manage sites to avoid conflicts among fishers, boaters, and divers. Despite the recognition of their importance, many aspects of MPA design and management, and relationships to other conservation measures, have not been studied such that science-based policy and management actions can be implemented. In particular, the study of fish populations in the marine environment is logistically difficult but in some cases can be greatly simplified by the use of newly emerging technologies. This project applies acoustic tracking technologies (using transmitters and receivers) to gather critical information on the area and habitat requirements of several species of marine fishes in the Florida Keys National Marine Sanctuary.

Fish Censuses

In the Florida Keys, "fishery-independent" sampling methodologies (meaning observations by scuba divers instead of using catch data) are increasingly being utilized to augment and enhance information derived from regional fishery fleets. The traditional reliance on "fishery-dependent" information (obtained from catch statistics) alone to determine the status of a stock has been shown to be fraught with statistical bias and reporting inaccuracies. In the last several years, fishery-independent sampling programs that are conducted across broad spatial scales, combined with long-term data sets over the last two decades, have contributed meaningful and timely results to resource managers in the Florida Keys National Marine Sanctuary and Dry Tortugas National Park. Specifically, visual censuses by scuba divers are used to assess reef fish biodiversity and population estimates to establish baseline information about the effectiveness of fishery management regulations, including MPAs. The primary objective of this project is to intensively test the variability of reef fish visual censuses over time and among habitat types at deep reef sites at Conch Reef.

Methods

Acoustic Studies

Intensive acoustic tagging efforts will be conducted using the Aquarius underwater laboratory and topside dayboat support. Fishes of several functional groups will be tagged: 20-30 pelagic omnivores (e.g. yellow tail snapper), 20-30 benthic piscivores (e.g. black grouper), and 20-30 grazers (e.g. parrotfish, species to be determined based on abundance at site) will be tagged with acoustic pingers. Fishes will be collected by hook and line at the surface and by traps deployed on the bottom from Aquarius. Surface-based tagging will occur initially at two locations: Conch Reef and at an offshore location in the vicinity of Grecian Rocks. Additional fish will be tagged opportunistically at other non SPA locations if extra tags are available. Coded and continuous acoustic pingers will be implanted in the peritoneal cavity through a small incision placed approximately 1 cm above the ventral midline (dependent upon size of the fish). Pilot studies were conducted in 2001 to evaluate the best way to handle and tag fish to minimize trauma to the fishes and maximize survival rates: tags cost $300 each so it's important that the fish survive the minor surgical procedure! An approved Animal User Permit covers this work through Dr. Kaufman and Boston University's Marine Program.

Tracking of tagged fish will be conducted during the August Aquarius mission, via diver-held receivers and seafloor mounted receivers. Observations will assess fish condition and habitat usage. Up to 40 acoustic receivers will be deployed both inside and outside Sanctuary Preservation Areas from Alligator Reef to Carysfort (2-4 receivers per site-shallow, moderate depth, and deep). A chart of the receiver deployment locations is available. Details regarding deployment of the receivers is presented under Environmental Impact (below). Data will be collected for individual tagged fish at each receiver on 1) the total number of days present, 2) the percent days present, 3) the number of visits, 4) the average residence time per visit, 5) day/night presence, and 6) any movement among reef sites. Further, the activity patterns and habitat use of individual fish will be quantified using the diver-held acoustic receivers during the August 2002 Aquarius mission. The data will be used as part of a dynamic computer model that simulates the role of MPAs for fish conservation and management. The model will also help assess the utility of MPAs of different sizes and shapes for managing species with different life history strategies and different associations with seafloor habitat.

Fish Censuses

Reef fish data will be collected by a stationary diver centered in a randomly selected circular plot. Divers sample 15 m diameter circular plots for five minutes attempting to count all fish observed within each imaginary cylinder extending from the bottom to the limits of vertical visibility (usually the surface). Divers begin each sample by facing in one direction and listing all species within the field of view. When no new species are noted, new sectors of the cylinder are scanned by rotating in one direction for the five minutes period. Several complete rotations were usually made for each plot. After the initial five minutes, data are then collected on the abundance and minimum, mean, and maximum lengths for each species sighted. Depth, bottom composition, estimated percentage cover, and maximum relief are recorded for each plot from the polar perspective of the centrally located observer. An all purpose tool, consisting of a 30 cm ruler connected perpendicularly to the end of a one-meter PVC pipe, is used as a reference device to reduce apparent magnification errors in fish size estimates. In usual operations, divers periodically calibrate their sample radius estimates with the meter stick or fiberglass tape. Species with few individuals (e.g. angelfish, barracuda, hogfish) are counted and their size estimated immediately. Highly mobile species that are unlikely to remain in the area (e.g. sharks, carangids, Clepticus parrai) are tabulated when first observed and then ignored. For common species (e.g. damselfish, wrasses, etc.) one 360 degree rotation is made for each species by working back up the list in reverse order of recording to reduce potential bias by avoiding counting a species when they were particularly abundant or obvious. The time required to record each sample averages 15-20 minutes (range 5 - 30), depending on the habitat.

Four stations will be established in each of three reef habitats (combination of reef class, e.g., spur and groove, and depth interval of 2-3 m) in the deeper waters (19-28 m) of Conch Reef. On a given day, two saturation divers will survey the four stations within a single habitat type during three different time periods: morning (7:45 to 9:45 am), midday (12 noon to 2 pm), and afternoon (4:15 to 6:15 pm). Each habitat will be sampled on three separate days over the course of the Aquarius mission. A concurrent study in three shallower water (7-14 m) habitats of Conch Reef will be conducted by SCUBA Nitrox surface divers.

Patchy Hard-Bottom in Sand: Low vertical relief (<0.5m) and complexity; sandy plain with patches of hard-bottom. Typically, the sand plain encompasses greater than 40% of the benthic coverage.

Low-Relief Hard-Bottom: Contiguous reef substrate characterized by low structural complexity and an absence of active reef accretion, typically by octocorals and algae. May be comprised of a mosaic of low-relief, limestone outcroppings interspersed with carbonate sediments.

Low-Relief Spur and Groove: Distinct coralline fingers or 'spurs' presently dominated by algae, but formerly consisting of coralline fingers constructed by staghorn coral and separated by sand grooves. Low-relief consists of broad individual spurs up to 5 m wide with 1 m vertical relief from the sand grooves to top of spur.

Reef Wall: Contiguous reef substrate of high vertical relief and complexity.

Reef Pinnacles: High-complexity structures that rise up to 10-15 m from the sea floor. These structures may occur in clusters and are typically surrounded by large sand plains.

Environmental Impact

Acoustic Studies

Installation of the receivers required placement of stainless steel rods (3/4 inch square x 4 feet long) into hard bottom reef structure. The receivers are attached to the rods using stainless bolts. A hydraulic drilling system was used to drill holes, 1.5 inch diameter x 12 inch deep, in nonliving hard bottom, into which steel rods were fixed using two-part epoxy. The epoxy hardens quickly and is much easier to work with than underwater cement. Damage to the bottom was minimized because hydraulic equipment works better and faster than pneumatic equipment, FKNMS and NURC staff are trained and competent using the drilling equipment, and site selection specifically targeted areas to avoid damage to living corals. Placement of the stainless steel rods is viewed as long-term (greater than two years) and far more attractive and stable, and potentially less damaging than deployments that utilize cement-filled tires or other "movable" structures placed on the bottom.

Fishing

Fish (approximately 12) will be caught prior to the August Aquarius mission using conventional capture and release methods for continuous pingers that will be monitored by aquanauts during the Aquarius mission to evaluate condition and habitat utilization. Fish will also be caught throughout the Aquarius mission for intermittent pingers that will be monitored using the receiver array previously deployed. Protocols developed in 2001 as part of a pilot effort were successful and minimized damage to or suffering by the fish. Surgical techniques are applied only by trained personnel and through approved guidelines established at Boston University (via Dr. Les Kaufman). Fish are placed in bait wells to anesthetize them prior to surgery (using MS-222) and to assist in their rapid recovery after the minor surgical procedure. Fish will also be caught for tagging using special traps deployed from Aquarius.

Fish Censuses

The circular plot method is non-destructive and provides reliable quantitative estimates of species composition, abundance (density per plot), frequency-of-occurrence, and individual size composition for the reef fish community. The Aquarius underwater habitat offers an unparalleled opportunity for the efficient use of research time.